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Nov. 1, 1966 M. HUROWITZ 3,283,256

"N" STABLE MULTIVIBRATOR Filed March 25, 1963 1N VENTOR MA RK HUROW/ TZ.

A T TORNE )1 United States Patent 0 M 3,283,256 N STABLE MULTIVTBRATQRMark Hurowitz, Palo Alto, (Ialifi, assignor to the United States ofAmerica as represented by the Secretary of the Army Filed Mar. 25, 1963,Ser. No. 267,870 11 Claims. (Cl. 323-147) This invention relates to amultivibrator circuit and more particularly to a multivibrator circuitthat has a plurality of stable states.

The invention relates specifically to a multivibrator circuit havingmore than two stages. The stages are connected together in such a mannerthat the addition of N active elements provides N stable states. Thesestates correspond to the condition of any one of the active elementsbeing turned on while the remaining active elements are off. The stablestates are exclusive because the stage that is turned on provides apotential that holds the remaining stage oif. Thus, at no time can morethan one stage be turned on.

Several different types of multi-stable multivibrator circuits areknown; however, generally speaking the number of stable stages islimited in the prior art devices and the stable states are not exclusivewhen more than two states are provided.

Therefore, an object of my invention is to provide a multivibratorcircuit having more than two stable states.

Another object of my invention is to provide a multivibrator circuitthat has as many stable states as there are active elements.

Another object of my invention is to provide a multivibrator circuitthat has N stable states.

A still further object of my invention is to provide a multivibratorcircuit that has N exclusive stable states.

These and other objects of the invention will become readily apparent byreferring to the following specification and accompanying drawing inwhich like parts in the various figures have like numerals and in which:

FIG. 1 shows the basic circuitry of a single tube stage of a bistablemultivibrator.

FIG. 2 shows the basic circuitry of a single stage of my invention.

FIG. 3 shows a multi-stable multivibrator circuit in accordance with myinvention.

FIG. 1 which shows a single tube stage of a basic multivibrator isincluded in this application only to illustrate how the well knownmultivibrator is modified to arrive at my invention; however, a briefdiscussion of this circuit may be helpful. The combination of resistors55 and 48 forms the basic D.C. coupling between stages. The outputvoltage E is adjusted to be approximately equal to the common stagevoltage E developed across the coupling impedance Z. A complete bistablemultivibrator is formed by taking a second tube stage essentiallyidentical to FIG. 1 and interconnecting the two stages in a well knownmanner.

As was stated above, a single stage of my N stable multivibrator is madeby modifying the circuit of FIG. 1. These modifications, as shown inFIG. 2, include the addition of resistors 33 and 42 and the addition ofa coupling network comprising diodes 21 through N 1 (where N is thetotal number of tube stages in the final circuit). If the input signalis applied directly to the grid of tube 1 3,2832% Patented Nov. 1, 1966rather than through resistor 33, only one resistor connected betweengrid and ground is necessary. My N stable multivibrator is arrived at byinterconnecting, in the manner shown in FIG. 3, N tube stagesessentially identical to the tube stage of FIG. 2.

The multivibrator shown in FIG. 3 has four identical tube stages, andtherefore, it has four stable states. Each stage has a triode, input andoutput circuits, and a diode coupling network. The cathodes of triodes 1through 4 are coupled to a negative 150 volt potential through commonresistor 47. Input signals E through E, are applied to the control gridsof triodes ll through 4 respectively. When one of the triodes isconducting, diode networks 57 through 6% operate to hold the remainingtubes cutoff. The diode networks each consist of three or (Nl) diodes(where N is the number of tube stages). The anodes of the diodes in eachnetwork are connected to the control grid of the associated triode. Forexample, the anodes of diodes 21, 22, and 23 in network 57 are connectedto the grid of triode l and the anodes of diodes 3d, 31 and 32. innetwork 6! are connected to the grid of triode 4. The plate of eachtriode is coupled through a variable and fixed resistor to the cathodeof one diode in each network except the diode network that has theanodes of its diodes connected to the grid of the same tube. Thus, theplate of triode 1 is coupled through fixed resistor 9 and variableresistor 13 to the cathodes of diodes 24, 27, and 3th in networks 58through 66 respectively. However, the plate of triode 1 is not coupledto any of the diodes in network 57; since, the anodes of these diodesare connected to the grid of this tube. A B+ potential of 300 volts iscoupled to the plates of triodes 1 through 4 via resistors 5 through 8respectively. A negative potential of 150 volts is applied to the outputnetworks of all the triodes. The various fixed potentials are soadjusted that the output voltage E of a given tube is greater than itsgrid voltage e when the tube is cut-off and less than its grid voltagewhen it is conducting. Neon lamps 37 through 45) give a visualindication of which stage is turned on.

The circuit shown in FIG. 3 has two modes of operation. It is operatedin one mode when the input signals are above the level required tochange states and is operated in the mode when the input signals arebelow the level required to change states.

With no input signals applied, all the tube stages start to conduct themoment the fixed potentials are applied; and an unstable balancedcondition exists. As soon as a random noise pulse from shot noise in thetubes, or from slight differences in the tube characteristics disturbsthis balanced condition one tube starts to draw more current than theothers. This slight unbalance cause the one favored tube to increase thebias of the others, tending to cut them off. This action continues untilthe favored tube is held full on while the other tubes are held full40fi.,

The operation just described is obtained by means of a D.-C. feedbackpath and applies not only to my N stable multivibrator but also to allbistable devices. Diode networks 57 through 60 provide the D.-C.feedback path in my circuit. The diode networks provide a path forapplying a negative bias to the tubes that are to be cutoff. This can beseen by assuming that one of the tubes, say triode 2, is the favoredtube. When triode 2 is conducting, diodes 21, 28, and 31 will be biasedin the forward direction, and the grids of triodes 1, 3, and 4- will bedriven more negative. As the grids of these triodes are driven morenegative their plates become more positive. The increased potential onthe plates of triodes 1, 3, and 4 back biases diodes 24, 25, and 26.Eventually triode 2 will be full on and the bias on triodes 1, 3, and 4will be sufficiently negative to hold these tubes off. When triodes 1,3, and 4 are off, the potential on the cathodes of diodes 24, 25, and 26will be positive; therefore, these diodes will be back biased and thegrid of triode 2 will be held more positive than its cathode. Since thegrid of triode 2 is held more positive than its cathode, triode 2 willremain on until it is turned off by an input signal or signals.

The circuit of FIG. 3 is now ready to receive input pulses in its firstmode of operation. In this mode of operation at least one of the inputsignals E 43 must be of suflicient amplitude to cause a change of stateor else nothing will happen. Of course, no change will take place, ifthe one pulse that is above the threshold required to cause a change ofstate is applied to the favored tube. The assumption was made earlierthat triode 2 is the favored tube; therefore, it will be assumed thattriode 1 is the only tube that receives a pulse whose amplitude is abovethe threhold level. Under these conditions, triode 1 will begin to drawcurrent and the series of events described above in reference to thefavored tube, will again take place; however, in this case triode 1 isturned on and held on while triodes 2, 3, and 4 are held off.

If all the input pulses E E are above the threshold value and not intime coincidence, the tubes will be turned on in sequence. The sequencewill be determined by the time relationship of the input pulses. Thetube receiving its pulse first will be turned on first.

If the input pulses E E are above the threshold value and in timecoincidence, the operation depends upon whether or not the pulses are ofequal amplitude. When the time coincident pulses are of equal amplitude,no change of state takes place. The favored tube remains on. When thepulses are not of equal amplitude, the tube receiving the largest pulsewill be turned on.

In the second mode of operation, the input pulses E -E are all below thethreshold level required to cause a change of state. Before any inputpulses are applied to the grids of the triodes, a measure pulse E isapplied to the cathodes of all the tubes. This measure pulse turns allthe tubes off. At the end of the measure pulse, the triode having thelargest input pulse applied to its grid is turned on. The fact that thecircuit operates in this manner when a measure pulse is applied to thecathodes of the triodes is apparent if the operation when no inputpulses are applied is recalled. At the end of the measure pulse all thetubes begin to conduct and an unsteady balanced condition exists. Theinput signals to the grids disturb this balance. The tube receiving thelargest signal on its grid will draw more current than the other tubesand eventually all the other tubes will be cut-off.

From the above discussion it is apparent that my circuit When operatedin its second mode compares the input signals and selects the one havingthe largest amplitude. My invention can also be used as a pulseamplitude comparator when operated in its first mode; however, in thiscase all the input signals to the grids must be coincident in time. Itwill, of course, be apparent to those skilled in the art that myinvention can be used for purposes other than amplitude comparison. Itwill also be apparent to those skilled in the art that variousomissions, substitutions and changes in form can be made to theembodiment shown and described without departing from the scope of theinvention. For example, transistors can be substituted for the triodesshown without changing the basic circuit configuration. Therefore, it ismy intention to be limited only as indicated by the scope of thefollowing claims.

What is claimed is:

1. An N stable multivibrator comprising: N electron tube stages, eachstage having a triode electron tube, a diode network, input circuitmeans, and output circuit means; means to connect the cathodes of allsaid triode electron tubes to a common point; means to apply separateinput signals to the input circuit of each of said triodes; and means tocouple the output circuit of each said electron tube to all but one ofsaid diode networks.

2. A multistable multivibrator circuit comprising: first, second, thirdand fourth triode electron tubes; means to apply separate input signalsto each of said electron tubes; a first, second and third diode; meansto couple the anodes of said first, second and third diode to the gridof said first triode; a fourth, fifth, and sixth diode; means to couplethe anodes of said fourth, fifth and sixth diodes to the grid of saidsecond triode; seventh, eighth and ninth diodes; means to couple theanodes of said seventh, eighth and ninth diodes to the grid of saidthird triode; tenth, eleventh and twelfth diodes; means to couple theanodes of said tenth, eleventh and twelfth diodes to the grid of saidfourth triode; means to couple the anode of said first triode to thecathodes of said fourth, seventh and tenth diodes; means to couple theanode of said second triode to the cathodes of said first, eighth andeleventh diodes; means to couple the anode of said third triode to thecathodes of said second, fifth and twelfth diodes; means to couple theanode of said fourth triode to the cathodes of said third, sixth andninth diodes; and means to connect the cathodes of all said triodes to acommon point.

3. An N exclusive stable state multivibrator comprising: N electrontubes each having a cathode, a grid, and an anode; means to connect thecathodes of all said electron tubes to a common point; means to applyseparated input signals to the grids of all said electron tubes; N diodenetworks each having (Nl) diodes; and means to couple the grids of eachsaid electron tubes through said diodes to the anodes of all the othersaid electron tubes.

4. An N exclusive stable state multivibrator comprising: N electrontubes each having a cathode, a grid and an anode; means to connect thecathodes of all said electron tubes to a common point; means to applyseparate input signals to the grids of all said electron tubes; N diodenetworks each having (N-1) diodes; means including said diode networksfor coupling the grid of each said electron tube to the anodes of allthe other said electron tubes; and means to simultaneously apply ameasure pulse to the cathodes of all said electron tubes.

5. A multivibrator circuit having N exclusive stable states comprising:N identical tube stages; each said tube stage having a triode electrontube, an input circuit, an output circuit, and (Nl) diodes; means tocouple the anodes of said (Nl) diodes of each stage to the input circuitof that stage; means to couple the input circuit of each stage to thegrid of the triode of that stage; means to connect the cathodes of thetriodes of all said stages to a common point; means to apply separateinput signals to the input circuit of each of said stages; and feedbackmeans including said (Nl) diodes of all said stages for coupling theoutput circuit of each said stage to the input circuit of all the otherof said stages.

6. A multivibrator circuit as described in claim 5 wherein a measurepulse is applied to said common point.

7. An N stable multivibrator comprising: N triode electron tubes; meansto couple the cathodes of all said triodes to a common point; means toapply separate input signals to each grid of all said triodes; andfeedback means for coupling the output of each of said triodes to thegrids of all the other triodes, said feedback means including N diodenetworks each having (Nl) diodes.

8. An N stable multivibrator comprising N amplitying devices each havingan input electrode, an output electrode and a third electrode; means toconnect said third electrode of all said amplifying devices to a commonpoint; means to apply separate input signals to said input electrodes ofall said amplifying devices; N-diode networks each having (N -1) diodes;and means including said diode networks for coupling the input electrodeof each said amplifying device to the output electrodes of all the otherof said amplifying devices.

9. An N stable multivibrator as described in claim 8 wherein a measurepulse is applied to said common point.

10. An 1 stable multivibrator as described in claim 8 wherein saidamplifying devices are transistors.

10 wherein a measure pulse is applied to said common point.

References Cited by the Examiner OTHER REFERENCES IBM Tech Dis-closureBul., volume 4, No. 9, February 1962, page 65.

MAYNARD R. WILBUR, Primary Examiner.

11. An N stable multivibr-ator as described in claim 15 JOHN MILLER:Examine"-

1. AN "N" STABLE MULTIVIBRATOR COMPRISING: "N" ELECTRON TUBE STAGES,EACH STAGE HAVING A TRIODE ELECTRON TUBE, A DIODE NETWORK, INPUT CIRCUITMEANS, AND OUTPUT CIRCUIT MEANS; MEANS TO CONNECT THE CATHODES OF ALLSAID TRIODE ELECTRON TUBES TO A COMMON POINT; MEANS TO APPLY SEPARATEINPUT SIGNALS TO THE INPUT CIRCUIT OF EACH OF SAID TRODES; AND MEANS TOCOUPLE THE OUTPUT CIRCUIT OF EACH SAID ELECTRON TUBE TO ALL BUT ONE OFSAID DIODE NETWORDKS.